PLANT TUMORS CAUSED BY WASPS IMPERILING PIN OAKS IN QUEENS AND L.I.

By KEITH SCHNEIDER

Published: October 24, 1985

Unsightly and destructive plant tumors caused by tiny wasps are threatening tens of thousands of pin oak trees in Queens and on Long Island.

The golf ball-size tumors, called horned oak galls, form after wasps have laid their eggs in the outer branches of the pin oaks. The galls disrupt the flow of nutrients, cause extensive defoliation and over a period of four to eight years can kill a tree.

The infestation is forcing horticulturists in New York City and on Long Island to try a number of pioneering and expensive methods to reduce wasp populations and control gall development.

Horned oak galls first appeared in the New York metropolitan region 20 years ago in pin oak trees lining streets of Bayside, Queens. At the time, however, arborists were battling Dutch elm disease and did not consider the oak gall a threat.

Since then the wasps have swept aross eastern Queens, Nassau County and parts of Suffolk County, devastating one of the more popular urban shade trees. Horned oak galls also have been found near Buffalo and Rochester, and in several other states, including New Jersey, Pennsylvania, Virginia, West Virginia, Ohio and Michigan.

''Long Island has the worst infestation,'' said Dr. Warren Johnson, a professor of entomology at Cornell University. ''There are trees out there that have so many galls, the branches literally weep under their weight.''

Entomologists estimate that 10 to 20 percent of Long Island's pin oaks have been attacked by the wasps. In some towns - Garden City, Mineola, New Hyde Park, Hicksville, Old Westbury, Upper Brookville, Old Brookville and Plainview - galls have formed on half of all pin oaks.

One of the more dramatic examples of the infestation has appeared along Old Country Road between Garden City and Plainview in Nassau County. Roughly 60 percent of the trees planted 25 years ago in a 30-inch strip between the road and the sidewalk have been attacked. Almost 10 percent are dead or near death. Trees that once displayed thick canopies are now bare and their branches bend under the weight of thousands of galls. ''It looks like a forest fire has been through here,'' said Joseph Savage, an entomologist with the Nassau County Cooperative Extension. ''All these trees are going out at the same time. This is a wipeout.''

Scientists are gaining greater understanding of the biological factors that have contributed to the destruction. The primary concern, they say, is the lengthy and unusual reproductive cycle of the cinipid wasp, an insect so small that two dozen could easily fit on a penny.

During the first week of July, adult female wasps emerge from the galls and lay eggs on the undersides of pin oak leaves. Within weeks, bumps form, each containing an immature wasp. In August, adult males and females hatch and swarm in the branches. Females then lay eggs in the outer branches before dying.

A Woody Knob

Over the next two years, the larvae feed on the tree's nutrients and produce hormones that react with plant proteins to form a woody knob. Several weeks before the wasps develop into mature adults, the galls develop sizable spikes, or horns. Each horn grows above a single insect. One gall can support 20 to 30 insects. When mature, the wasp crawls through the horn, chews off the tip and flies away to repeat the reproductive cycle.

In the hardwood forests of the eastern United States, cinipid wasps generally present few problems because the insects are not strong fliers. In forests where maples, beeches and other oaks are mixed with pin oaks, the wasp is unable to enlarge its territory easily.

The wasp has been able to increase its urban range because of a biological mistake made by arborists decades ago, when pin oaks were first planted in Queens and on Long Island. In the 1950's and 1960's, urban designers favored planting one type of tree along city streets to gain a uniform look. Arborists in many cities chose the pin oak because it was the fastest-growing oak, generated a sizable canopy for shade and was thought to be relatively immune to disease and pests.

''The pin oak was considered to be a good, clean tree that would survive on the streets,'' said Richard Wickey, general supervisor of the Garden City Parks Department.

A Break for the Wasp

But by planting hundreds of thousands of pin oaks side by side, arborists created a single-species monoculture. The wasps took advantage of the genetic uniformity. After becoming established in one pin oak, the weak-flying wasp easily swept into the next tree, and the next, until miles of streets and avenues were infested.

Across the metropolitan region, specialists are trying to halt the spread of the wasp with a number of experimental programs. Last spring, for example, the New York City Parks and Recreation Department spent more than $60,000 pruning branches from the most heavily affected trees along Utopia Parkway, Francis Lewis Boulevard, and 73d Avenue in Queens. Some pin oaks were shorn of nearly all their branches. A similar program in Garden City cost $15,000.

''Our intent was to remove the galls before the wasps emerged,'' said William Hubbard, the Parks Department horticulturist in Queens. ''We went out to inspect the other day, and we found the trees are making a good comeback. They're not gall-free. But we hope that by reducing the wasp population, we'll reduce the problem.''

Highly Toxic Insecticide

Munsey Park officials recently injected infested pin oaks with a highly toxic insecticide called bidrin. The injection method, which involves inoculating the tree with a teaspoon of insecticide every spring for three years, also has been used in Buffalo and Rochester with some success.

''We've tried it on 50 or 60 trees, and it's worked 90 percent of the time,'' said Richard H. Stedman, the president of Tree Inject Systems of Clarence Center, a suburb of Buffalo.

And arborists are removing dead pin oaks and replacing them with maples, Bradford pear trees and sycamores. The goal is to mix up the urban forest and reduce the number of pin oaks on which the wasp can feed.

Photo of Keith Savage inspecting a pin oak tree on Old Country Road in Plainview, L.I. (NYT/Barton Silverman)